What tools do I need for build a steel pergola frame from rhs?

This guide includes a comprehensive tools list. Key welding & fabrication tools are detailed in the Tools Required section.

What Australian Standards apply to a welded steel pergola?

The principal standards are AS 4100 for steel design, AS/NZS 1170.2 for wind actions, AS/NZS 1554.1 for structural welding and AS/NZS 5131 for fabrication and erection. The National Construction Code and state or territory building laws also apply. The engineer’s drawings and project specification determine the applicable compliance requirements.

What size RHS should be used for a steel pergola?

There is no single compliant RHS size for every pergola. An engineer must consider span, frame spacing, roof weight, wind region, terrain, shielding, connection capacity and footing conditions. A 75 × 75 × 3.0 mm SHS post may suit some designs, but it is not a universal specification or substitute for structural calculations.

Can galvanised RHS be welded safely?

Galvanised RHS can be welded only with effective fume controls and suitable preparation. Remove the zinc coating from the weld zone, provide local exhaust ventilation, keep the welder’s breathing zone clear of fumes and follow the safety data sheet. After welding and inspection, restore corrosion protection using a coating system suitable for the exposure environment.

Does a steel pergola need council approval in Australia?

A steel pergola may require planning approval, a building permit or both, depending on its area, height, setbacks, roof coverage, location and state or territory rules. Exempt-development limits differ between jurisdictions. Confirm the requirements with the local council or relevant building regulator before ordering steel, excavating footings or fixing anchors.

Can a steel pergola be fixed directly to an existing concrete slab?

An existing slab should not be assumed to support pergola posts or wind-uplift loads. Its thickness, reinforcement, edge distances, concrete strength and footing arrangement must be verified. Post-installed anchors should be selected and designed in accordance with AS 5216 where applicable, using the anchor manufacturer’s installation requirements and the engineer’s connection details.

How to build a steel pergola frame from RHS

Building a steel pergola frame using Rectangular Hollow Section (RHS) and Square Hollow Section (SHS) creates a durable, modern, and fire-resistant outdoor entertaining area suited to the harsh Australian climate. This guide walks you through setting out, cutting, welding, and finishing stru

Quick answer

A steel RHS pergola should be set out from engineered drawings, cut and tack-weld square, temporarily braced, welded to the specified procedure, anchored to designed footings and corrosion-protected. Member sizes cannot be chosen by appearance alone; wind actions under AS/NZS 1170.2 and steel design to AS 4100 determine the required sections and connections.

Skill level: Intermediate
Time: 2–3 weekends (approx. 20–30 hours total)
Trade: Welding & Fabrication
Updated: 6 November 2026

Tools you will need

MIG/GMAW Welder: Minimum 180A
Angle Grinder: 125mm
Cold Cut Saw / Metal Drop Saw: With carbide
Clamping Gear: Minimum 4x heavy
Drilling Equipment: Rotary hammer drill

🔥 Steel Pergola Frame Fabrication: DIY RHS Build Guide

How do you build a steel pergola frame from RHS?

Building a steel pergola frame using Rectangular Hollow Section (RHS) and Square Hollow Section (SHS) creates a durable, modern, and fire-resistant outdoor entertaining area suited to the harsh Australian climate. This guide walks you through setting out, cutting, welding, and finishing structural steel sections in compliance with local residential standards. While welding steel offers unmatched structural integrity, care must be taken with joint fit-up, corrosion protection, and engineering compliance.

What skill level is required to fabricate an RHS pergola?

Intermediate — Estimated time: 2–3 weekends (approx. 20–30 hours total) Note: Due to the structural nature of overhead structures, all load-bearing welding must align with the quality expectations of AS/NZS 1554.1 (Structural Steel Welding). Building approvals and engineering certification are legally required in most Australian council jurisdictions before construction.

What tools are required to cut, weld and install an RHS pergola?

🔧 Equipment Required

MIG/GMAW Welder: Minimum 180A–200A inverter MIG welder (multi-process or dedicated MIG capable of running solid wire with shielding gas). Angle Grinder: 125mm (5-inch) grinder with ultra-thin 1.0mm cutting discs, flap discs (40/80 grit), and wire wheel. Cold Cut Saw / Metal Drop Saw: With carbide-tipped blade or abrasive disc for square, accurate cuts. Clamping Gear: Minimum 4x heavy-duty F-clamps, 2x 90-degree corner welding clamps, and locking C-clamps. Measuring & Layout: 8m steel tape measure, engineer’s square, combination square, string line, and spirit levels (both 600mm and 1800mm magnetic levels). Drilling Equipment: Rotary hammer drill (for slab/footing anchors) and magnetic base drill or heavy-duty bench drill press with cobalt/HSS hole saws for steel fixing holes.

What steel sections, fasteners and coatings are required for a pergola frame?

Columns (Posts): 75 x 75 x 3.0mm SHS (Grade C350LO or C450LO Duragal/pre-galvanised mild steel) or 89 x 89 x 3.5mm SHS depending on span. Main Bearers/Beams: 100 x 50 x 3.0mm RHS (Grade C350LO). Rafters/Purlins: 75 x 50 x 2.0mm RHS or 75 x 50 x 2.5mm RHS. Base Plates & Cleats: 10mm mild steel flat bar cut to size (e.g., 150 x 150 x 10mm base plates). Welding Consumables: 0.9mm AWS A5.18 ER70S-6 solid MIG wire paired with Argoshield / Autoshield (Argon/CO₂/O₂ mix) or 0.9mm E71T-11 gasless flux-cored wire for outdoor on-site repairs. Fasteners: M12 Grade 8.8 hot-dip galvanised structural bolts, nuts, and washers; M12 galvanised concrete screw anchors (e.g., AnkaScrews) or chemical studs for footings. Corrosion Protection: Zinc-rich cold galvanising paint spray (e.g., Galmet ColdGal) and an etch primer/polyurethane topcoat system.

Safety Requirements

⚠️ Safety Mandatory Requirements
Welding PPE: Auto-darkening welding helmet compliant with AS/NZS 1338.1 (set to shade 10–11 for 130–180A MIG), heavy-duty split-cowhide welding gloves, and a flame-retardant (FR) welding jacket or leather sleeves. Eye & Ear Protection: Class 5 earmuffs/plugs and clear impact-rated safety glasses (AS/NZS 1337) worn under the welding hood and during all grinding/cutting operations. Galvanised Steel Fume Hazard: Pre-galvanised RHS/SHS off-gases toxic zinc oxide fumes when welded, which causes severe metal fume fever. Mandatory: Strip galvanising back at least 25–50mm from all weld zones using a coarse flap disc, and use a P2-rated particulate respirator fitted with a nuisance odour filter, alongside adequate mechanical cross-ventilation or local fume extraction. Fire Safety: Keep a certified 4.5kg ABE dry chemical fire extinguisher adjacent to the work area. Clear a 10m radius of dry grass, timber offcuts, and combustible materials. Implement a mandatory 30-minute fire watch after the final arc is extinguished. Overhead Safety: Hard hat and steel-capped work boots compliant with AS/NZS 2210.3. Never stand underneath unbraced, temporarily propped steel sections.

Step-by-Step Guide

Step 1: Council Approvals, Engineering & Site Layout

1️⃣ Check Local Regulations and Mark Out Footings

Pergolas attached to a dwelling or exceeding specific roof areas (generally over 10–20m², depending on your local state/council planning scheme) typically require a Development Application (DA) or Complying Development Certificate (CDC). Engage a structural engineer to confirm member sizing against Australian wind loads (AS 4055 / AS/NZS 1170.2).

Set out your perimeter using timber batter boards, string lines, and the 3-4-5 triangle method to establish a square boundary. Check diagonal measurements—they must be identical. Mark footing locations directly on the ground or slab.

Step 2: Base Plate Fabrication & Post Footing Prep

2️⃣ Cut and Drill Anchor Plates

Cut your 10mm plate into 150 x 150mm squares. Mark and drill four corner holes to accept M12 structural concrete anchors, keeping hole centres at least 35mm in from plate edges.

Prepare your 75 x 75 x 3.0mm SHS posts. Grind back the protective coating to bright, bare steel 30mm up from the bottom end. Clamp the base plate flush and square to the post bottom.

Set your MIG welder:

Process: GMAW (MIG) Wire: 0.9mm ER70S-6 Gas: Argon / 16-18% CO₂ mix at 15 L/min Voltage: 21.5V – 22.5V Wire Feed Speed: approx. 7.5 – 8.5 m/min

Tack weld on all four sides. Deposit a continuous 6mm fillet weld around the entire perimeter of the post-to-plate connection using a slight push angle (10–15°), ensuring full fusion into the heavy 10mm base plate without undercutting the thinner 3.0mm wall.

Step 3: Cutting & Prepping Main Bearers and Posts

3️⃣ Precision Mitres and Weld Joint Prep

Measure finished post heights, factoring in roof fall/pitch (minimum 1:100 fall for flat pergolas to shed water, or 5° minimum for corrugated metal roofing). Cut your posts to height using a metal drop saw to ensure square cuts.

For your 100 x 50 x 3.0mm RHS bearers, determine whether you are running top-mounted beams (posts beneath beams) or face-welded connections with internal sleeves/cleats. Top mounting provides optimal direct gravity load transfer. Cap the tops of the SHS posts with 75 x 75 x 3mm steel plates or weld 100 x 50mm beam seating plates directly to the post heads.

Grind all mill scale and factory duragal coatings back to clean, shiny parent metal on all joint interfaces.

Step 4: Fit-up, Tacking, and Welding the Main Frame

4️⃣ Tacking and Distortion Management

Erect and brace the upright posts temporarily using prop legs and structural clamps. Anchor the base plates loosely to your slab or footings using your M12 anchors. Use an 1800mm spirit level to plumb each post in both planes.

Lift the 100 x 50 x 3.0mm RHS main bearers into place. Clamp tightly using heavy F-clamps. Check levels across all beams.
Deposit solid 15–20mm tacks on opposing sides of each connection. Re-check for square by measuring corner-to-corner diagonals. Weld the structural joints using sequence welding (jump from joint to joint) to avoid excessive heat buildup and thermal warping. Maintain your travel speed to achieve a uniform, slightly convex weld face meeting AS/NZS 1554.1 SP standards.

Step 5: Fabricating and Installing Rafters

5️⃣ Notching, Cleating, and Installing Infill Sections

Cut the 75 x 50 x 2.0mm RHS rafters. If sitting the rafters flush inside the outer frame, fabricate 50 x 50 x 5mm angle cleats or 6mm flat bar tabs, stitch-welded inside the bearer web. Pre-drill cleats to allow rafters to be through-bolted, or tack and fully weld the rafters directly into the frame.

For welding 2.0mm RHS to 3.0mm RHS:

Voltage: 18.5V – 19.5V Wire Feed Speed: 5.5 – 6.5 m/min Direct the welding arc primarily toward the thicker 3.0mm section, washing the puddle gently onto the 2.0mm wall to prevent burn-through.

Step 6: Post-Weld Cleaning & Corrosion Protection

6️⃣ De-slagging, Grinding, and Cold Galvanising

Allow all welds to cool naturally in ambient air; do not quench with water, as this hardens the heat-affected zone (HAZ) and increases crack susceptibility.

Run a mechanical wire wheel or flap disc over all completed welds to remove silicon islands and spatter. Wipe down every welded joint with wax and grease remover or acetone. Liberally apply a high-solids zinc-rich cold galvanising coating (minimum 93% zinc dust in dry film) to all raw and heat-affected zones in 2–3 thin coats, bridging the original galvanised protective layer. Once cured, apply an exterior-grade structural steel primer and topcoat (e.g., direct-to-metal polyurethane) to match your home's aesthetic.

Common Mistakes to Avoid

1.Welding Directly Through Galvanised Coatings: Attempting to weld over zinc without grinding it back leads to porosity, lack of root fusion, heavy spatter, and severe risk of zinc fume inhalation. Always grind to bare metal.

2.Omitting Adequate Bracing During Fabrication: Structural steel frames expand and contract under heat. Failing to cross-brace the posts and beams prior to final welding results in twisted, out-of-plumb pergolas that cannot be pulled straight once cooled.

3.Undersizing Wall Thickness: DIY builders often buy 1.6mm furniture-grade tube to save money. This tube is prone to burn-through during welding and will not meet Australian structural wind-uplift requirements. Stick to a minimum of 2.5mm–3.0mm for primary columns and load-bearing beams.

4.Neglecting Water Drainage In Enclosed Hollow Sections: Completely sealed RHS/SHS frames without drain/weep holes can collect condensation internally over years, causing uninspected internal structural corrosion. Ensure end caps are 100% seal-welded to exclude moisture, or include a 6mm weep hole at the lowest point.

Pro Tips
💡 The Anti-Spatter Advantage: Coat your workpieces with water-based anti-spatter spray before running your beads. Spatter rolls straight off the factory zinc coating instead of baking into it, drastically reducing post-weld cleanup. 💡 Heat Sink Backing for Thin Walls: When welding 2.0mm RHS rafter joints, clamp a scrap copper block or heavy steel flat bar behind open joints where possible. This acts as a heat sink, letting you achieve full penetration without blowing through edges. 💡 Pre-Drill on the Ground: Drill all fixing holes (rafter cleats, batten brackets, wire trellises, or downpipe brackets) on your bench before hoisting steel overhead. Drilling overhead into high-tensile steel on a ladder is exhausting and dangerous. 💡 Use Temporary Alignment Stitches: Instead of full tacks on visible exterior faces, tack your RHS frames on the inside or bottom faces first. If a measurement shifts out of square, a small inside tack is easily split with a 1.0mm cutting disc without damaging the architectural outer faces.

Recommended Tools

🔧 Recommended Equipment
UNIMIG Viper 185

Frequently asked questions

What is involved in build a steel pergola frame from rhs?: Building a steel pergola frame using Rectangular Hollow Section (RHS) and Square Hollow Section (SHS) creates a durable, modern, and fire-resistant outdoor entertaining area suited to the harsh Australian climate. This guide walks you through setting out, cutting, welding, and finishing stru
What skill level do I need for build a steel pergola frame from rhs?: Intermediate — Estimated time: 2–3 weekends (approx. 20–30 hours total)
What are common mistakes when build a steel pergola frame from rhs?: 1. Welding Directly Through Galvanised Coatings: Attempting to weld over zinc without grinding it back leads to porosity, lack of root fusion, heavy spatter, and severe risk of zinc fume inhalation. Always grind to bare metal. 2. Omitting Adequate Bracing During Fabrication: Structural steel frames expand and contract under heat. Failing to cross-brace the posts and beams prior to final
What tools do I need for build a steel pergola frame from rhs?: This guide includes a comprehensive tools list. Key welding & fabrication tools are detailed in the Tools Required section.
What Australian Standards apply to a welded steel pergola?: The principal standards are AS 4100 for steel design, AS/NZS 1170.2 for wind actions, AS/NZS 1554.1 for structural welding and AS/NZS 5131 for fabrication and erection. The National Construction Code and state or territory building laws also apply. The engineer’s drawings and project specification determine the applicable compliance requirements.
What size RHS should be used for a steel pergola?: There is no single compliant RHS size for every pergola. An engineer must consider span, frame spacing, roof weight, wind region, terrain, shielding, connection capacity and footing conditions. A 75 × 75 × 3.0 mm SHS post may suit some designs, but it is not a universal specification or substitute for structural calculations.
Can galvanised RHS be welded safely?: Galvanised RHS can be welded only with effective fume controls and suitable preparation. Remove the zinc coating from the weld zone, provide local exhaust ventilation, keep the welder’s breathing zone clear of fumes and follow the safety data sheet. After welding and inspection, restore corrosion protection using a coating system suitable for the exposure environment.
Does a steel pergola need council approval in Australia?: A steel pergola may require planning approval, a building permit or both, depending on its area, height, setbacks, roof coverage, location and state or territory rules. Exempt-development limits differ between jurisdictions. Confirm the requirements with the local council or relevant building regulator before ordering steel, excavating footings or fixing anchors.
Can a steel pergola be fixed directly to an existing concrete slab?: An existing slab should not be assumed to support pergola posts or wind-uplift loads. Its thickness, reinforcement, edge distances, concrete strength and footing arrangement must be verified. Post-installed anchors should be selected and designed in accordance with AS 5216 where applicable, using the anchor manufacturer’s installation requirements and the engineer’s connection details.

Written by Welder, the Welding & Fabrication specialist at VIC.Tools.